Blackening is generally used, for the purpose of increasing visibility, as a method for roughening (diffusion of light) or blackening (absorption of light) a surface of a metal layer by treating with acid or alkali or by plating to eliminate scattered reflection of light and raise light absorption. For example, if a blackened layer is formed on a metal mesh for shielding electromagnetic wave generated from a PDP, reflection of light from the electromagnetic shielding metal is inhibited and an image on the display can be therefore seen with high contrast.
Currently commercialized methods of forming blackened conductive patterns can be representatively divided into a photolithographic method and a screen printing method. In the photolithographic method, a flexible base film made by pressing a thin plate of conductive material onto a polyethylene (PE) or polyester (PET) film is used. In order to form a pattern circuit, a dry film or a photoresist solution is coated on the surface of the conductive material and a film to be realized to the circuit is compacted onto the dry film or photoresist solution coated layer, followed by UV irradiation, thereby transferring the circuit. After development using a developing solution, unnecessary conductive thin plate is etched using a chemical etching solution with the circuit to be realized alone being remained, and the dry film or coated photoresist solution compacted on the surface of the circuit is then removed to fabricate patterns. The resulting conductive patterns are brought into contact with blackening material to form blackened conductive patterns.
However, the aforementioned conventional photolithography method has problems that the fabrication process is complex and winding, crumpling or tearing may be generated due to an adhesive layer used for the film during transporting process of the fabrication. Also, high cost and large sized equipments are required according to the etching process and environmental problem may be caused during disposal of the etching solution.
In the screen printing, another method of forming and blackening conductive patterns, a conductive paste is screen printed to form conductive patterns and thereon blackening material is formed or a conductive paste containing the blackening material is screen printed, thereby forming the blackened conductive patterns. The method of conductive patterns by the screen printing has simple processes, but represents limitation to form high resolution patterns of below 30 um and large area patterns and also has problems of high cost equipment and low productivity.
In recent, in order to form the high resolution patterns of below 30 um, there has been studied a method using a laser.
Japanese Patent Publication No. 2002-314227 discloses a method for manufacturing a ceramic circuit board, in which holes corresponding to conductive patterns is formed on a film adhered to a green sheet by laser processing, a conductive paste is filled in the through hole and thereafter the film adhered to the green sheet is removed, thereby forming thin fine conductive patterns. Japanese Patent Publication No. 2004-281738 discloses a method for drawing conductive wire patterns by adhering a conductive paste to a substrate through laser scanning, in which the surface of a the substrate on which a conductive paste is coated is scanned by laser beams to form conductive wire patters by curing the conductive paste and thereafter the portion of the conductive paste excluding the portion scanned by the laser beams is solved by an organic solvent to removed the same and the portion scanned by the laser beams is then calcined to draw conductive the wire patterns on the substrate.
Japanese Patent Publication No. 2006-222295 discloses a method for ultrafine wiring board on which ultrafine wirings are formed, in which a photoresist resin formed on a board is subject to an interference exposure by irradiating a laser beam, followed by development, and thereafter, a solution containing conductive material is filled in the bottom of the groove portion and sintered, thereby forming ultrafine wirings.
Also, US Patent Publication No. 20060057502 discloses a conductive wiring pattern by laser irradiation, in which a board is applied with metal dispersion colloid including metal nanoparticles of 0.5 nm-200 nm diameters, a dispersion agent and a solvent, partially irradiated by a laser beam of 300 nm-550 nm wavelengths to sinter the metal nanoparticles and then washed to eliminate metal dispersion colloid on the portion not irradiated by the laser beam, thereby forming the conductive circuit corresponding to the shape irradiated by the laser beam.
Although various methods of forming fine patterns using a laser are disclosed as described above, a method of forming blackened fine patterns has not yet been disclosed.